The Knowledge

Of QBasicAbigail Joyce C.Purisima

Enelrah Vanna T. Dela Cruz

Grade 9 SSC - Lavoisier

Mr. Angel CoronaSubject Teacher

BASIC stands for

Beginner’s All Purpose Symbolic

Instruction Code. It was invented in

1963, at Dartmouth College, by the

mathematicians John George

Kemeny and Tom Kurtzas.

QBASIC is an interpreter which

means it reads every line and

translates it.

QBasic (Microsoft Quick Beginners All purpose Symbolic Instruction

Code) is an IDE and interpreter for a variant of the BASIC programming

language which is based on QuickBASIC. Code entered into the IDE is

compiled to an intermediate form, and this intermediate form is immediately

interpreted on demand within the IDE. It can run under nearly all versions

of DOS and Windows, or through DOSBox/DOSEMU, on Linux and FreeBSD. For

its time, QBasic provided a state-of-the-art IDE, Including a debugger with

features such as on-the-fly expression evaluation and code modification.

QBasic interfaceThis chapter gives a brief overview of the QBasic interface.

The interface has the following features:

1. Window displaying the current program2. Menu3. Name of current program4. Window to immediately execute a command

5. Status bar6. Status of Caps Lock and Number Lock7. Current line of cursor8. Current column of cursor

Parts of QBASIC Status bar

The status bar is at the

bottom of the screen. It

displays a short list

commands

(<Shift+F1=Help>

<F6=Window> <F2=Subs>

<F5=Run> <F8=Step>).

Name of current

program

The file name of the current

program is displayed near the

top of the screen in the

center. You can change the

name by selecting "Save As"

on the "File" menu.

Current line

On the right side of the status

bar, the current line of the

cursor is displayed.

Current column

On the right side of the status

bar, the current column of the

cursor is displayed

Current programThe current program displayed in the middle of the screen,

and covers most of the Qbasic interfere.

MenuThe menu provides most of the operation for the Qbasic

editor. Such as opening a file, pasting text, and searching for a

string.

FileNew - Clears the current program

Open - Loads a program from disk

Save - Saves the current program to disk

Save As - Saves the program, but under a

different name

Print - Prints the selected text, current

window, or entire program

Exit - Closes the QBasic interpreter

EditCut - Removes the selected text and stores it in

the clipboard

Copy - Copies the text instead of removing it

Paste - Adds the text in the clipboard to the

current position of the cursor

Clear - Removes the text without storing it to the

clipboard

New Sub - Enables you to create a new

subroutine (see Subroutines and Functions)

New Function - Enables you to create a new

function (see Subroutines and Functions)

Search Find - Allows you to search for a string

of text in the program

Repeat Last Find - Continues the

previous search operation

Change - Replaces each instance of a

string with another string

SUBs - Shows the list of current subroutines

and functions (see Subroutines and Functions)

Split - Displays the contents of the current

program in two windows. If the window is

already split, this hides the second window

Output Screen - Shows the QBasic output

screen.

View

RunStart - Executes the current program

Restart - Starts from the beginning

Continue - Continues execution at the

current position

OptionDisplay - Enables you to change display colors,

the number of spaces to use for

tabs, and whether or not scroll bars are visible

Help Path - The location of the QBASIC.HLP file

Syntax Checking - Allows you to have the

QBasic editor check the syntax of your

program as you type

Debug Step - Processes the next command

Procedure Step - Processes the next

command, does not show QBasic going

inside a subroutine or function

Trace On - Shows the command that is

being executed while the program is

running

Toggle Breakpoint - Sets or removes a

breakpoint.

Set Next Statement - Allows you to

continue execution at the specified lineHelpIndex - List of all QBasic commands,

keywords, operators, etc.

Contents - The table of contents for QBasic

help

Topic - Show help for a specific keyword

Using Help - Displays information on using

QBasic help

About - Shows information about the QBasic

interpreter

Programming in QBasic Of all of high level languages, BASIC (Beginners All purpose Symbolic Instruction Code)

is probably the easiest to learn. The beginning user soon discovers that small programs

can be written and quickly entered into the computer, producing interesting results. The

goal of our study is to learn how to write computer programs in QBASIC Language.

QBASIC DATAData is a collection of facts and figures that is entered into the computer through the

keyboard. Data is of two types:

CONSTANT: Data whose value does not

change or remains fixed.

(a) NUMERIC CONSTANT: Numbers -

negative or positive used for mathematical

calculations

e.g. –10, 20, 0

(b) ALPHANUMERIC CONSTANT / STRING:

Numbers or alphabets written within double

quotes(inverted commas “ “).

e.g. “Computer”, “Operating System”

VARIABLE: Data whose value is not constant

and may change due to some calculation.

(a) NUMERIC VARIABLE: Holds a Numeric

Constant for arithmetic

calculations (+, - ,*, / )

e.g. A = 50

(b) ALPHANUMERIC VARIABLE: Must end

with a $ sign and the

Alphanumeric constant must be enclosed in

inverted commas.

e.g. Name$ = “Alkansha”,

TYPES OF MODE IN QBASICOnce QBASIC program is loaded into the computer memory, it displays Ok prompt. Ok

means it ready to accept the commands.

QBASIC can be made to translate your instructions in two modes:

• Direct Mode• Program Mode

Direct Mode: The accepts single line

instructions from the user and the

output is viewed as soon as enter key is

pressed.

The instructions are not stored in the

memory. This mode can be used to do

quick calculation. They do not have line

numbers.

E.g.

Print 3+4

Print “This is the Direct mode in

QBasic”

Program Mode: The mode is used to type

a program which is stored in the memory.

They have line numbers . We have to give

the command to get the output.

e.g.

10 Print 3+4

20 End

RUN

Arithmetic ExpressionsExpressions are used in QBASIC in order to perform calculations. in general ,an expression

may consist of a single constant or a single variables, or of arithmetic operation involving

two or more constants or two or more variables ,or of any arithmetic combination of

constants and variables. Although complicated mathematical expressions will not occur

frequently, some skill is required to translate mathematical expressions into QBASIC

expressions. in performing this task ,it is necessary to know that the QBASIC compiler

using the following order of precedence in performing arithmetic operations:

Order Symbol Remarkfirst ( ) Operations within

parentheses are

performed first.

second ^ Exponentiation is

performed before other

arithmetic operations.

third *, / Multiplication and

division are equal in

order of precedence.

fourth + , - Addition and

subtraction are

performed last and are

equal in order of

precedence.

Example

Suppose( a=5. b=4 ,c=2 ,i=2,j=1)

Execute the following expressions in order of precedence:

? a + b + c / 12 -------------9.67

?(a + b+ c) / 12-------------0.92

? a + b / c – I * j + a ^ 2----30

? a * b – c / I + j + a ^ b + c ^ 3--------653

Suppose that ( a=10. b=8 ,c=2 ,i=23,j=89)

? a * j ^ b – I / c * j + 20

? j / ( I + c )

?j / I +c

TRY This!!!

The IF and THEN commands

The IF and THEN commands are used to compare an

expression and then perform some task

based on that expression.

x = 5

IF x = 5 THEN PRINT "x equals 5"

Since X does equal 5 in this case,

Output:

x equals 5

Expression signs

You can also enter the following statements,

instead of the equals sign:

x < 5 (x is less than 5)

x > 5 (x is greater than 5)

Run the following:

x = 16

IF (x > 5) THEN PRINT "x is greater than 5"

Output:

x is greater than 5

You can also combine the signs like this:

x <= 5 (x is less than or equal to 5)

x >= 5 (x is greater than or equal to 5)

x <> 5 (x does not equal 5)

Run the following example:

CLS

x = 5

IF (x >= 5) THEN PRINT "x is greater

than or equal to 5"

IF (x <= 5) THEN PRINT "x is less

than or equal to 5"

IF (x <> 5) THEN PRINT "x does not

equal 5"

Output:

x is greater than or equal to 5

x is less than or equal to 5

ELSE

Using the ELSE command, you

can have the program perform

a different action if the

statement is false.

x = 3

IF x = 5 THEN PRINT "Yes"

ELSE PRINT "No"

Since X doesn't equal 5,

Output:

No

END IF

END IF allows you to have multiple

commands. END IF should appear right after

the list of commands.

x = 5

IF (x = 5) THEN

INPUT a$

PRINT a$

END IF

The following program uses ELSE with the

END IF command:

x = 16

IF (x = 5) THEN

INPUT a$

PRINT a$

ELSE

PRINT x * 2

END IF

Output:

32

ELSE IF

The ELSEIF command allows you to

perform a secondary action.

x = 6

IF (x = 5) THEN

PRINT "Statement 1 is true"

ELSEIF (x = 6) THEN

PRINT "Statement 2 is true"

END IF

Output:

Statement 2 is true

Multiple expressions

You can have more than one expression

in IF...THEN by using either the OR

operator or the AND operator.

The OR operator only requires one

expression to be true in order to print

"Yes" in the following program:

x = 20

IF (x = 5 OR x = 20) THEN PRINT "Yes"

Output:

Yes

The AND operator requires both

expressions to be true.

x = 7

IF (x > 5 AND x < 10) THEN PRINT

"True"

Output:

True

This is a slightly more complex

example:

x = 16

y = 3

IF ((x > 5 AND x < 10) OR y = 3) THEN

PRINT "Correct"

Output (since Y is 3):

Correct

You can have more than one expression in IF...THEN by

using either the OR operator or the AND operator.

The OR operator only requires one expression to be

true in order to print "Yes" in the following

program:

X=21

IF x

Now Try this!!!

You can have more than one expression in IF...THEN by

using either the OR operator or the AND operator.

The OR operator only requires one expression to be

true in order to print "Yes" in the following

program:

X=3002

IF x

Adding documentation to your programs

Documenting your program (also called

"commenting") allows you to remind

yourself about something in your

program. Plus, if your program is seen

by other people, documenting can help

them understand your code.

The REM (remark) command enables you

to add comments to your program

without the text

being treated like an instruction.

CLS

PRINT "Some text"

REM This text is ignored.

REM This program clears the

output screen,

REM and then prints "Some

text."

TIP: You can use an apostrophe

instead of the REM command.

You can add REM to the same line as another command by placing a colon after

the first instruction.

CLS: REM This command clears the screen

PRINT "Text": REM This command prints "Text" to the screen

PRINT 534: REM This prints the number 534 to the screen

NOTE: If you use an apostrophe instead of REM while doing this, you do not need

to add a colon.

CLS ' This command clears the screen

PRINT "Text" ' This command prints "Text" to the screen

PRINT 534 ' This prints the number 534 to the screen

Reading and writing to files

To save data to a file:

1. Call the OPEN command, specifying the file name, file mode (OUTPUT), and

file number.

2. Use PRINT, followed by the file number and the data you want to write.

3. Close the file using the CLOSE command.

The following opens a file, using mode OUTPUT and number 1, and then

saves the text Hello World! to the file:

OPEN "testfile.dat" FOR OUTPUT AS #1

PRINT #1, "Hello World!"

CLOSE #1

To open a file for "reading," call OPEN and pass INPUT as the file mode.

Then you can read the data by using the INPUT command.

OPEN "testfile.dat" FOR INPUT AS #1

INPUT #1, text$

CLOSE #1

PRINT text$

Output:

Hello World!

Guessing game

The following is a simple guessing game:

CLS start:

PRINT "Guess a number between 1 and

10: ";

INPUT num

IF (num < 1 OR num > 10) THEN

PRINT "That is not between 1 and 10"

GOTO start

END IF

IF (num = 6) THEN

PRINT "Correct!!!"

ELSE

PRINT "Try again"

PRINT

GOTO start

END IF

Output (may be slightly different):

Guess a number between 1 and 10:

? 2

Try again

Guess a number between 1 and 10:

? 7

Try again

Guess a number between 1 and 10:

? 6

Correct!!!

Our own example of Guessing game

Program

Output

The Knowledge

Of QBasicAbigail Joyce C.Purisima

Enelrah Vanna T. Dela CruzGrade 9 SSC - Lavoisier

Mr. Angel CoronaSubject Teacher